Sismic can be installed using pip as usual: pipinstallsismic.
This will install the latest stable version.
Sismic requires Python >=3.4.
You can isolate Sismic installation by using virtual environments:

Get the tool to create virtual environments: pipinstallvirtualenv

Create the environment: virtualenv-ppython3.4env

Jump into: sourceenv/bin/activate

Install Sismic: pipinstallsismic

The development version can also be installed directly from its git repository:
pipinstallgit+git://github.com/AlexandreDecan/sismic.git@devel